Reaction zone control

ABSTRACT

The method and means of controlling the output of a multi zone reaction installation about a desired conversion level and at optimum performance conditions. An input to the reaction installation is regulated to regulate the severity of reaction in individual zones and such regulation is controlled by means including a regulatable set point for each reaction zone. The discharge effluent from the downstream reaction zone is analyzed and the signal responsive to the character of such effluent is used first to determine a performance index output signal and secondly for determining the total conversion level. An optimizer utilizes the performance index output signal to determine a first output signal for each reaction zone representing a first component of each regulatable set point. The optimizer analyzes the performance index output signal and then determines a first output signal necessary for each reaction zone to approach an optimum performance in the reaction zones. A controller utilizes the signal indicative of the conversion level of the reaction zones and determines a second output signal representing a second component of the regulatable set points corresponding to the desired total conversion level of the reaction zones. The first and second output signals are combined and are utilized as the regulatable set points for controlling the regulation of the severity of reaction in each reaction zone.

United States Patent 1191 Boyd [ Sept. 18, 1973 REACTION ZONE CONTROL David M. Boyd, Clarendon Hills, 111.

[73] Assignee: Universal Oil Products Company, Des Plaines, Ill.

[22] Filed: May 24, 1971 [21] Appl. No.: 146,400

[75] Inventor:

[56] References Cited UNITED STATES PATENTS 3,497,449 2/1970 Urban 235/l5l.l2 X 3,257,363 6/1966 Miller et al. 235/l5l.l2 UX 3,321,280 5/1967 Trotter, Jr. et al. 235/l5l.l2 X 3,402,212 9/1968 Gantt 260/669 R 3,458,691 7/1969 Boyd, Jr.... 235/151.12 3,594,559 7/1971 Pemberton 235/1501 X Primary ExaminerJoseph F. Ruggiero Att0rneyJames R. Hoatson, Jr. and Ronald H. Hausch [57] ABSTRACT The method and means of controlling the output of a Optimizer P darn/once Index (P1) Dararminarar l l.. 1 V "P! Signal 1 I 26 I 1 multi zone reaction installation about a desired conversion level and at optimum performance conditions. An input to the reaction installation is regulated to regulate the severity of reaction in individual zones and such regulation is controlled by means including a regulatable set point for each reaction zone. The discharge effluent from the downstream reaction zone is analyzed and the signal responsive to the character of such effluent is used first to determine a performance index output signal and secondly for determining the total conversion level. An optimizer utilizes the performance index output signal to determine a first output signal for each reaction zone representing a first component of each regulatable set point. The optimizer analyzes the performance index output signal and then determines a first output signal necessary for each reaction zone to approach an optimum performance in the reaction zones. A controllerutilizes the signal indicative of the conversion level of the reaction zones and determines a second output signal representing a second component of the regulatable set points corresponding to the desired total conversion level of the reaction zones. The first and second output signals are combined and are utilized as the regulatable set points for controlling the regulation of the severity of reaction in each reaction zone.

14 Claims, 4 Drawing Figures PATENIED SEP 1 8 ma SHEET2DF3 \VV 2. m -m F Mm. 38:05 mm km J QEQ QEQ i INVENTOR: DAV/D M. BOYD ATTORNEYS The present invention is directed to control of the reaction zone severity in a continuous flow reaction process wherein a charge stock is passed through at least two reaction zones at conversion conditions and the resulting product effluent is analyzed. The analysis therefrom is used to determine a performance index and a total conversion level. Controller means is utilized to control the reaction zone severity orrate of reaction to maintain the conversion level. Optimizer means is litilized to optimize the performance index and the signal derived from the optimizer means is used in conjunction with the signal from the controller means to adjust the reaction zone severity. Typical of applicable conversion processes is catalytic hydrore'forming, wherein a naphtha fraction is passed into a reaction zone containing noble metal catalysts, in the presence of molar excess of hydrogen. Another hydrocarbon conversion process which may utilize the concept of this invention is the dehydrogenation of ethylbenzene to styrene.

Otherprocesses which may be utilized in connection with the present invention control system include any reaction processes such as thermocracking, catalyticcracking, thermo hydrocracking, catalytic hydrocracking, isomerization, alkylation, polymerization, and the like.

. BACKGROUND'OF THE INVENTION As understanding of thereaction mechanisms occurring within a reforming zone has increased, it has become possible to adjust operating techniques and catalyst compositions to enhance the specific reaction declization of paraffinic hydrocarbons to produce corresponding aromatic hydrocarbons; (3) the hydrocracking of high molecular weight hydrocarbons to produce lower molecular weight hydrocarbons, and (4) the isomerization of normal paraffinic hydrocarbons to produce branched chainedisomers of equal molecular weight. I

Each of these four reaction mechanisms upgrade low octane hydrocarbons to high octane hydrocarbons, but it has become necessary to adjustoperating techniques in order to control the reaction mechanisms selectively to maximize octane with minimum loss of liquid product yield and minimum product production of paraffinic gas (methane, ethane, and propane). It has thus been determined that the dehydrogenation of naphthenes to aromatics. is promoted by operating at low pressure levels; the dehydrocyclization of paraffins to aromatics is promoted by low pressure and high temperature; and hydrocracking of paraffins is promoted by high pressure, high temperature, and high residence time of the charge stock on the catalystfand that isomerizationof paraffins is promoted by intermediate temperature, and a catalyst comprising a much higher halogen content than normally employed. Since aromatic hydrocarbons have higher octane ratings than other bydrocarbons of equivalent molecular weight, catalytic reforming has shown a current tendency to operate at higher temperatures and lower pressures in order to enhance the resulting gasoline octane rating by increasing the aromatic hydrocarbon content of the gasoline.

I Therefore the catalytic reforming unit producing high octane motor fuel, typically is maintained at operating conditions sufficient to enhance the dehydrogenation of naphthenes and the dehydrocyclization of paraffins in order to maximize the production of both aromatics and hydrogen, maximum hydrogen being desired since it is normally consumed elsewhere in the typical petroleum refinery. The production of aromatic hydrocarbons is enhanced by catalytic reforming at a temperature in the range of from about 850 F to about 1,050 P and at a pressure in the range of from about psig to about 400 psig when the end boiling point of the charge stock is about 350 F, but when the end point of the charge stock is about 400 F or more, the pre ferred pressure is about 500 psig in order to maintain catalyst stability.

The operator of the catalytic reforming unit judiciously selects the operating conditions which he believes will most economically produce the desired high octane gasoline. The naphtha charge stock is passed into the reaction zone under conditions of temperature,

pressure, catalyst composition, hydrogen to hydrocarbon ratio, etc. which will produce a reactor effluent having the composition necessary to result in the desired high octane product. When analysis indicates that the product does not meet octane specification, it is normal in the art for the operator to manually change conditions within the reaction zone tocompens ate for any deviation from specification.

The resulting hot vaporous reactor effluent containing hydrogen, normally gaseous hydrocarbons and gasoline boiling range hydrocarbons is withdrawn from the reaction zone, cooled, condensed, and passed to a separation zone which is normally a single stage gravitytype phase separator maintained at reforming pressure of, say, 50-500 psig. The liquid hydrocarbon or unstabilized reforrnate phase is in equilibrium therein with the gas phase containing a major proportion of the hydrogen. The hydrogen-rich vapor phase is withdrawn and a portion thereof is recycled to the inlet of the catalytic reforming zone for circulation across the catalyst together with the naphtha charge. The liquid hydrocarbon phase from the separator is then ultimately fed to a distillation zone which normally comprises a stabilizer column. The liquid phase contains a substantial portion of dissolved hydrogen and C -C hydrocarbons which must be removed in order that the stabilized reforrnate will meet vapor pressure and octane number specifications. A typical sample of catalytic reformate from a separator operating at 250 psig consists of:

Component s C,-400"F endpoint The overhead from the stabilizer column is predominately C and lighter hydrocarbons, and the column bottoms is stabilized gasoline typically comprising predominately C to about 400 F endpoint material.

Usually, reforming reaction zones are run with excessive heat input in order to guarantee that the octane quality of the reformate gasoline will meet specification. Then that result is that the resulting reformate will actually exceed specifications with respect to octane a good part of the time. This mode of operation increases the refiners cost, since, as those skilled in the art know, decrease in product yield accompanies increase in the product octane number.

Prior attempts have been made to continuously control the heat input to a reforming reaction zone to maintain a predetermined octane quality of the liquid yield of the reaction zone. However, if the reaction severity is increased without regard to the yield there is always a danger that the resulting yield loss will far out strip the resulting value of the octane enhancement of the yield. Thuswe have found that we can maintain product of desired octane number and optimum performance conditions by controlling the severity of each reaction zone with controllers having regulatable set points. The set points will comprise a signal proportional to the desired octane value of the product yield as well as signals which optimize the liquid yield of the reforming reaction zones.

In the dehydrogenation of ethylbenzene to the styrene, a mixture of ethylbenzene and steam is passed over a fixed bed of dehydrogenation catalyst. In order to heat the reactants to reaction temperature, it is the general practice to admix the ethylbenzene, which is usually at temperatures significantly below reaction temperature,'with steam which has been superheated to a temperature above the reaction temperature so that the admixture is at reaction temperature as it passes over the dehydrogenation catalyst. Since the basic chemical reaction involved, namely the dehydrogenation of ethylbenzene to styrene, is endothermic there is a significant decrease in the reaction zone temperature as the reaction proceeds. Naturally, as the temperature decreases, the rate of the reaction also decreases so that the overall conversion percentage of ethylbenzene in the process declines to a point where it would be economically unattractive. The temperature of the superheated steam may be increased so that the temperature between the inlet temperature of the reactants and the outlet temperature of the reaction products average equals the required reaction temperature. However, it is noted that at higher temperatures when the superheated steam is admixed with ethylbenzene, the ethylbenzene undergoes, to some extent decomposition or cracking through a pyrolytic reaction. in many instances such pyrolysis is effected to a degree that the process becomes uneconomical due to the loss of ethylbenzene to toluene, benzene, as well as the products of carbon monoxide, carbon dioxide, polymeric materials, tars, and the like. Prior art has suggested means for increasing the level of conversion by utilizing stepped beds and introducing a separate stream of steam between such catalytic beds or zones in order to reheat the reactants to reaction temperature. These schemes do have merit and in fact do increase efficiency of conversion. However, it is still desirable that those skilled in the art be furnished with an improved method for the conversion of ethylbenzene SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide the method and means of controlling the severity of reaction zones by maintaining the desired conversion level throughout such zones and by optimizing a performance index thereof.

Another object of this invention is to provide the method and means of controlling a continuous hydrocarbon conversion process.

It is another object of this present invention to provide the method and means for controlling a continuous flow hydrocarbon process which adjusts the severity of conversion through optimizing a performance index and maintaining a conversion level.

It is another object of this invention to provide for the method and means for controlling the dehydrogenation of ethylbenzene to styrene;

It is another object of the present invention to provide an improved method and means of controlling a continuous conversion process responsive to the octane number of the effluent liquid hydrocarbon discharged from the reaction zone and responsive to the optimization of the total liquid yield of the hydrocarbon discharged. 7

In one of its broadest aspects the present invention provides for in combination with at least two reaction zones having inlet means for introducing an inlet effluent therein and outlet means for discharging the resultant outlet effluent therefrom, a control system which maintains a desired total conversion level of operation and which optimizes the performance thereof comprising: (a) regulating means connected to eachreaction zone for regulating the severity of reaction therein; (b) a control means connected to each regulating means for controlling, the regulation thereof, each control means including a regulatable set point; (c) analyzing means communicating with the effluent of the downstream reaction zone for producing a signal responsive to the character of the outlet effluent; (d) performance indicating means connected to said analyzing means for determining a performance index output signal; (e) optimizer means connected to the performance indicating means for optimizing the performance of said reaction zones, said optimizer means including means for determining a first output signal for each control means representing a first component of the aforesaid regulatable set points and including computer means for analyzing the performance index output signal of said performance indicating means to determine a first output signal necessary for eachreaction zone to approach an optimum performance of said reaction zones; (1) controller means connected to said analyzing means for determining a second output signal representing a second component of the aforesaid regulatable set points corresponding'to the desired conversion level of said reaction zones; (g) means connected to said optimizer means, to said controller means, and to said control means for combining each first output signal with the second output signal to thereby generate signals representing each aforesaid regulatable set point.

In one embodiment, the performance index output signal is comprised of a function of 1) the undesirable products in the outlet effluent with respect to (2) the desirable products in the outlet effluent. Thus, the performance index signal may comprise the ratio of undesirable products in the outlet effluent to the desirable products in the outlet effluent. The optimizer means will then determine a first output signal for each control means to approach a minimum value of this particular ratio. The regulating means may include means to regulate the heat input to each reaction zone; however, this should not be considered limiting upon the present invention. For example, the pressure may be controlled to vary the severity of each reaction zone in the vessel. In the alternative the amount of an input fluid may be regulated to control the severity of reaction.

The conversion level may be determined by a function of the desired products in the outlet effluent with respect to the unreacted reactants remaining in the ef fluent. On the other hand, if dealing with a particular vessel such as a reforming reaction vessel, the conversion level may be determined by the octane rating of the liquid outlet effluent.

Another aspect of the present invention provides for a method of controlling the operation of at least two connecting reaction zones comprising the steps of: (a) regulating the severity of reaction within each reaction zone; (b) controllingsuch regulation in response to a regulatable set point signal for each reaction zone; (0) analyzing the outlet effluent of the downstream reac tion zone to produce a signal responsive to the character of said outlet effluent; (d) determining a performance index output signal from the signal derived from step (i c); (e) optimizing the performance of said reacbining each first output signal with the second output.

signal to thereby generate each aforesaid regulatable set point signal. 1

Again, the performance index output signal may be comprised of a function of undesirable products in the outlet effluent in respect to the desirable products in the outlet effluent. The conversion level may be determined by a function of thedesired products in the out let effluent with respect to the unreacted reactants remaining in the outlet effluent or on the other hand it may be determined by the octane rating of the outlet effluent. The severity of reaction may be regulatedby regulating the heat input to each reaction zone, the pressure of each reaction zone, the amount of input effluent to the reaction zone, and the like.

A specific embodiment of this inventionprovides for from, a method of controlling such process which comprises the steps of: (a) regulating the severity of reaction within each catalytic reaction zone; (b) controlling such' regulation in response to a regulatable set point signal for each reaction zone; (0) analyzing the outlet effluent of the downstream reaction zone to produce signals responsive to: (1) the quantity of benzene in said outlet effluent, (2) the quantity of toluene in said outlet effluent, (3) the quantity of styrene in said outlet effluent, and (4) the quantity of ethylbenzene in said outlet effluent; (d) determining a performance index output signal from signals (1), (2), and (3) of step (c), the value of said performance index output signal being given by a function of: (l) the sum of the quantities of benzene and toluene with respect to (2 the quantity of styrene; (e) optimizing the performance of the catalytic reaction zones by analyzing the performance index output signal of step (d) and determining a first output signal necessary for each reaction zone to approach an optimum performance of said reaction zones, said first output signals representing a first comin connection with the process of dehydrogenating ethylbenzene wherein ethylbenzene admixed with steam is passed through at least two catalytic reaction zones and a total outlet effluent including the desired product styrene, the less desirable products of benzene and toluene, and unreacted ethylbenzene is discharged thereponent for each of the aforesaid regulatable set point signals; (f) determining the total conversion level of said reaction zones from signals (3) and (4) of step (c), the value of said total conversion level being given by a function of: (1) the quantity of styrene with respect to,-(2) the quantity of ethylbenzene in the outlet effluent; (g) determining a second output signal representing a second component of the aforesaid regulatable set point signal whose value is determined by the comparison of a desired conversion level to the actual conversion level determined in step (f); (h) combining each first output signal of step (e) with the second output signal of. step (g) to thereby generate each aforesaid regulatable set point signal.

Preferably the performance output signal is derived from a signal determined by the ratio of the sum of quantities of benzene and toluene to the quantity of styrene in the outlet effluent. Thus, the first output signals determined by analyzing and optimizing the performance output signal is determined by minimizing this ratio. The conversion level is preferably given by the ratio of the quantity of stryene to the quantity of ethylbenzene in the outlet effluent. Thus, if it is desired to maintain percent ratio of styrene to ethylbenzene in the outlet a proportional controller or the like may be utilized to determine a second output signal representing a second component of the regulatable set points by a comparison of the conversion level determined in step (1) and a desired conversion level of 80 percent. The preferred mode of regulating the rate of reaction or the severity of reaction utilizes means which regulates the input of steam to the reactor. This may comprise control valves, pumping and the like connectable to the inlet steam means.

Another specific embodiment of the present invention is related to the process of reforming hydrocarbon charge stocks wherein the hydrocarbon charge stock is passedthroug'h at least two catalytic reaction zones and a a total product effluent is discharged therefrom. The invention provides for a method of controlling such a .process which includes the steps of: (a) regulating th ing the outlet effluent of the downstream reaction zone to produce signals responsive to: (l) the liquid yieldin said product effluent and (2) the octane value of the liquid yield; (d) optimizing the performance of the reaction zones by analyzing signal (1) of step (c) and determining a first output signal necessary for each reaction zone to approach an optimum performance of said reactor, each first output signal representing a first component of the aforesaid regulatable set point signals; (e) determining a second output signal representing a second component of the aforesaid regulatable set point signals whose value is determined by the comparison of the desired octane value of the liquid yield and the octane value determined in step (c); and, (f) combining each first output signal of step (d) with the second output signal of step (e) to thereby generate each aforesaid regulatable set point signal.

The present invention may now be more clearly understood by reference to the accompanying drawing which sets forth simplified schematical flow diagrams of typical reactor systems in which particular embodiments of the inventive control system are utilized.

FIG. 1 illustrates schematically reaction apparatus having two reaction zones wherein the heat input to each zone controls the regulation of the rate of reaction or severity of reaction.

FIG. 2 illustrates schematically hypothetical performance curves of a reactor installation.

FIG. 3 illustrates schematically a typical reactor system which may be utilized for the dehydrogenation of ethylbenzene to styrene and which uses the control system of the present invention.

FIG. 4 illustrates a catalytic reforming unit wherein the heat input to two reaction zones is used to regulate the reaction severity.

DESCRIPTION OF THE DRAWING With reference now to FIG. 1 there is shown a simplified schematical flow diagram for a typical reaction installation. Reactors 1 and 1' may be one of the many reactors utilized in reaction processes as for example catalytic reforming, ethylbenzene dehydrogenation, thermocracking, catalytic cracking, thermo hydrocracking, catalytic hydrocracking, isomerization, alkylation, polymerization and the like. Reactor 1 has inlet means 2 for introducing the inlet effluent therein. A

heater 4 is provided in conjunction with inlet 2 and may be any type of heat exchanger employing any type of heating medium such as steam, hot oil, hot vapor flue gas, etc. In the embodiment of FIG. 1 the heater 4 is a direct fired furnace having a burner 5 which is supplied through line 6 with fuel. The reaction mixture or effluent is heated within coils 7 in heater 4.

The heated reaction mixture leaves heater 4 via line 2 and is passed into reaction zone 1 at a pressure which of course will depend on the particular reaction desired. The effluent from reaction zone 1 is discharged through outlet 3 and is passed through downstream reheater 4 of similar configuration as heater 4. The reacted mixture leaves this heater and is passed into reaction zone 1' via inlet 34. The total reaction zone effluent is discharged through outlet line 3 for storing or further processing. The regulation of the rate of reaction or severity in the reactors in this particular embodiment is by the heat input into each reaction zone. The heat input to the reaction zone is provided by introducing a fuel via lines 6 and 6' into the combustion burners 5 and 5 within heaters 4 and 4'. Fuel, which may be liquid or gas is burned within the combustion zones and the hot combustion gases pass through the furnaces and out the stacks. As the fuel is burned and the combustion gas passes through furnaces, the necessary heat is put into the reaction mixture contained within coils 7 and 7 by means of radiation and convection.

The heat input into the reaction mixture is controlled and adjusted by varying the flow of fuel to combustion burners 5 and 5. This control of flow of fuel is achieved by means of a flow control loop contained in lines 6 and 6. The flow control loop comprises control valves 8 and 8' and flow sensing means 9 and 9', which for illustrative purposes are shown as orifices. Flow signal lines 10 and 10' transmit the flow signal from each orifice 9 and 9' to flow controllers 12 and 12'. Flow controllers 12 and 12 then transmit an output signal to the control valves 8 and 8' via lines 13 and 13. The set point of fiow controllers l2 and 12 is automatically adjustable or regulatable.

Temperature controllers l4 and 14' also with automatically adjustable set points, sense inlet temperature of reactors, as detected by thermocouples or other sensing means 15 and 15' located in inlet lines 2 and 34 of the reactor. The resulting temperature output signals are transmitted from temperature controllers 14 and 14 to flow controllers 12 and 12 via lines 17 and 17' to adjust or reset the set points of flow controllers 12 and 12 respectively. I

An analyzer 18 is installed to be in communication with the outlet effluent of the downstream reactor 1 via line 19. Line 19 represents a suitable sampling system to provide a continuous sample of the outlet effluent of the reactor installation. The sample is withdrawn from line 3 and is passed into analyzer 18 for analysis. The analyzer of FIG. 1 should be constructed to include analyzing means capable of producing a signal or signals responsive to the character of the outlet effluent. The analyzer may include analyzers such as chromatographs, continuous octane monitors, as well as continuous flow monitors which determine the total flow through outlet 3. At least two outlet signals are determined by analyzer 18 and will include a signal representing a particular conversion level and a signal to be utilized for determining a performance index of the reactor. The conversion level output signal is transmitted via line 20 to a recorder controller 21. Controller 21 has a set point which is adjustable and which is adjusted to the preferred conversion level. As for example, if the conversion level is to be determined by the octane value of the liquid yield in line 3, controller 21 will have a set point corresponding to the desired octane value of the outlet effluent in line 3. The output signal from the controller 21 is transmitted via line 23 through summing amplifiers 24 and 24'. The output signal from the summing amplifiers 24 and 24', which will be the total signal from controller 21 and from an optimizer 30 is transmitted via lines 25 and 25 to the set points ofthe temperature controllers 14 and 14.

As set forth previously, analyzer 18 will also be capable of determining a signal or signals to be utilized for determining a performance index of the reactor installation. For example, the optimizer may be a chromatograph which would generate a signal determinate of the amounts of undesirable products in the outlet efiluent and a signal determinate of the desirable products in the outlet effluent. These two signals may be transmitted via lines 26 and 27 to a performance index determination device 28. On th other hand, if the signal determined by the analyzer 18 is a performance signal capable of being optimized in itself, it may be transmitted directly to the optimizer 30. Performance index determination device 28 may be an operational amplifier capable of determining a function of the signals from the analyzer which is indicative of the performance of the reactor and which is capable of being optimized. By way of example, performance index determination device 28 may be an operational amplifier capable of determining the ratio of the signal representing the quantity of undesirable products in the reaction effluent to the signal representing the quantity of the desirable products in the reaction effluent. This signal is transmitted via transmitting means 29 to the optimizer 30. The optimizer has means for determining an output signal for the control means of each reaction zone which are then transmitted via lines 31 and 33 to the summing amplifiers 24 and 24' respectively. Thus, the output signals in lines 31 and 33 representing first components of the set points of the temperature controllers and the output signal of line 23 representing a second component of the set points for the temperature controller are combined in summing amplifiers 24 and 24' and transmitted to the set points of the temperature controllers via lines and 25. The optimizer has computer means to determine th performance index output signal of line 29 and to determine the output signal necessary for each reaction zone to approach an optimum performance in the reactor vessels. Optimizer is a device well known in the art which maximizes or minimizes some measure of process performance. By way of example, assume that the reactors performance index may be determined by the ratio of undesirable products to desirable products in the product effluent and this ratio will vary with the heat input to each reaction zone. It is noted that the ratio for each reaction zone goes through a minimum at point where the slope of the curve is zero as shown in FIG. 2 of the drawing. If zone 1 is operating at the position as shown as point a on the curve, and zone 1 is operating at point d of its curve the optimizer computer will determine the output sig nals necessary to alter the set points of the respective temperature controllers so that the ratio of undesirable products to desirable products will approach b, and 2 respectively, the minimums on the curves. Likewise, if point c is the point on th curve which zone 1 is operating, and f is the point in the curve where zone 1 is operating, the optimizers computer will determine output signals necessary so that the severity of each reactor zone will approach 12 and e respectively on the curves. It makes no difference if an optimum actually exists or at which point it exists. The optimizer adjusts its outputs to improve the performance. Reference may be made to pages 22-52 through 22-54 of Perrys Chemical Engineering Handbook, fourth edition, published by McGraw-Hill Book Company for a brief description of optimizer theory.

There are various types of optimizers on the market, including the Motorola Veritrak performance optimizer controller manufactured by Motorola, Instrumentation and Control Inc. of Phoenix, Arizona, a subsidiary of Motorola, line. This particular optimizer is an analogue computer that operates on the principle of introducing small output changes and noting the effect on the index or indices it scans. By noting the effect, it can reach a decision to change the output signals necessary to approach an optimum performance of the reiii actor. The performance index it scans need not be the index of each reaction zone for the optimizer. It may be set up to only scan the performance index of the total reaction zone defined by zones l and l although theoretically the optimizer may scan more than one performance index. If only scanning the total performance index, preferably the small perturbations or changes in each reaction zone are made out of sequence with each other. By making the perturbations out of sequence, the optimizer can more readily differentiate which perturbation in which reaction zone caused the performance index to change and thus make its decision as to each reaction zone.

If the conversion level of the reaction installation can be defined by a ratio of desired products in the product effluent outlet 3 to the unreacted reactants in the product effluent outlet upon a change in this number the analyzer output signal 20 will transmit a new signal. Controller 21 will transmit an output signal in transmitting line 23 to the summing amplifiers 24 and 24'. This signal would be a second component of the temperature controller set points and would correspond to a value which would make the total reaction severity lie within the desired conversion level. Preferably the decisions of controller 21 are made out of sequence with any changes made by the optimizer so the causes of any changes in the performance index: are recognizable. If the ratio of undesired products to desirable products in the product effluent conduit 3 is indicative of the performance of the reactor, analyzer 18 will be of the type that can analyze such quantities and transmit signals indicative thereof. These signals will be transmitted via line 26 and 27 to a performance index determination device which would be an operational amplifier capable of determining and transmitting a signal representing the ratio of undesirable products to desirable products in the outlet effluent. This output signal would be transmitted to the optimizer 30 via line 29 and the optimizer would determine the output signals that would cause the reaction severity of each reaction zone to ap proach a ratio of undesirable products to desirable products corresponding to a minimum. This signal would be transmitted via line 31 and 33 to summing amplifiers 24 and 24 where the signal from line 23 would be added to any existing from signal line 23. The two combined signals would make up the set points of the temperature controllers 14 and 14' which would in turn adjust the set points of the controllers I2 and 12' thus affecting the heat input to each reaction zone.

Referring now to FIG. 3 of the drawing there is again shown a reactor 51 which in this particular embodiment is a three stage reactor having catalyst zones A, B, and C. This particular reactor is. useful for the dehydrogenation of ethylbenzene to styrene. The catalyst employed for this dehydrogenation reaction is preferably an alkali-promoted iron catalyst. Typically, such a catalyst may consist of percent by weight ferrous oxide, 2 percent by weight of chro-mia, 12 percent by weight of potassium hydroxide, and 1 percent by weight of sodium hydroxide. Other catalyst compositions include percent by weight iron oxide, 4 percent by weight chromia, and 6 percent by weight potassium carbonate. While these known commercial dehydrogenation catalysts are preferred, other known catalysts may be used, including those comprising ferrous oxide-potassium oxide, other metal oxides and/or sulfides, including those of calcium, lighium, strontium,

magnesium, beryllium, zirconium, tungsten, molybdenum titanium, hafnium, vanadium, aluminum, chromium, copper, and mixtures of two or more including chromia-alumina, alumina-titania, alumina-vanadia, etc. Similarly, the various methods of preparing the aforesaid catalysts are well known within the prior art.

The amount of catalyst contained in each catalyst bed may be varied considerably. Usually, the amount of catalyst is expressed in terms of bed depth which may range from 6 inches to 50 to 60 feet, depending upon such conditions as alkylated aromatic hydrocarbon feed rate and the amount of heat which therefore must be added to effectuate the reaction at an economical rate. Typically, the bed depth may range from 2 feet to 6 feet.

The reactor pressure may also be varied over a considerable range. Preferably a slightly superatmospheric pressure, e.g., 4-20 psi g, is used; although, in some cases, subatomspheric or significant super-atmospheric pressure may be desirable. Sufficient pressure must be maintained at the reactor inlet to overcome the pressure drop through the multi-beds of catalyst contained in the reactor vessels or in separate vessels if each such bed is contained in a separate reactor. Although the preferred arrangement of the reaction zones for styrene production is shown as multiple beds contained in a single reactor, single beds in multiple reactors, may be used in the practice of this invention.

As the reactants contact the catalyst contained in, for example, the first catalyst bed, there is a temperature and pressure decrease observed across the catalyst bed due to the endothermic nature of the reaction and due to the pressure drop characteristics of the reactor design including the presence of catalyst therein. For example, without additional heat being required, the temperature of the effluent leaving the first catalyst bed would probably be in the order of 100 F or more, less than the inlet temperature selected for the combined charge material to the first catalyst bed. Similarly, depending upon the amount of catalyst contained in the first reaction zone, the pressure of the effluent from the first catalyst bed preferably would be less than 10 psig lower than the selected pressure for the combined charge to the first catalyst bed. Typically, the pressure drop through the first catalyst bed would be within the range from 2 to 6 psig and if a similar pressure drop were observed across, for example, three catalyst beds, the total pressure required at the inlet of the first catalyst bed would be significant, e.g., in the range from 6 to 18 psig. Superheated steam at a temperature of about l,400 F is introduced into the inlet 52 to the reactor via steam line 85 at a ratio of about 0.65 pounds of steam to 1.0 pounds of ethylbenzene and is admixed with the ethybenzene to a nominal temperature of about 1,200 F (as defined in the prior art the dehydrogenation of ethylbenzene is generally affected at a reactor temperature within the range of about 932 to 1,292 F). A second steam line 85' is used to introduce superheated steam at a nominal temperature of about l,500 F in between catalyst zones A and B at a ratio of about 1.0 to 1.2 pounds of steam to effluent to raise the temperature of the total effluent to reaction temperatures. A third steam line 85" is used to introduce super-heated steam at a nominal temperature about 1,500 F into admixture with the total effluent between zones B and C at a ratio of about 0.80 to 1.35 poundsof steam to effluent to raise the temperature of the effluent to reaction temperatures. The total outlet effluent having a temperature within the range of about l,000 to 1,400 F is discharged through outlet conduit means 53.

A flow control loop is provided for each steam inlet to vary the flow of steam into the reactor at each point of introduction to thus control reaction zone severity. The flow control loop comprises flow control valves 58, 58' and 58" receiving output signals via lines 53, 53' and 53" from flow controller 62, 62' and 62" respectively. Flow controllers 62, 62' and 62" receive the flow rate signals from sensing means 59, 59' and 59" via flow signal lines 60, 60 and 60" respectively. Flow controllers 62, 62 and 62" have adjustable set points which are reset by the output signals of temperature controllers 64, 64 and 64" respectively, said output signals being transmitted via line 67, 67 and 67 Each temperature controller receives a temperature signal from the inlet of each reactor zone A, B, and C respectively by means of temperature sensing devices such as thermocouples 65, 65 and 65 Temperature controllers 64, 64' and 64" also have adjustable set points.

The product effluent from outlet 53 is sampled by an analyzer 68 by means of a sampling loop 69. The analyzer 68 may be a chromatograph capable of determining output signals of the products and/or reactants in the outlet effluent. For styrene production, the output signals which are utilized in the present invention are: quantity of benzene; quantity of toluene; quantity of styrene; and quantity of ethylbenzene. These signals are transmitted via lines 86, 87, 88 and 89 respectively to four input memory amplifiers 35, 36, 37 and 38 respectively. Preferably, the signal that the memory amplifiers will accept will indicate only the peak height of these products benzene, toluene, styrene and ethylbenzene although filtered or average values are contemplated. The output of the styrene memory amplifier 37 and ethylbenzene memory amplifier 38 are transmitted via lines 43 and 44 to a divider 45 and the quotient output signal representing the ratio of styrene to ethylbenzene is transmitted to a recorder controller 71 via line having a set point adjusted to the desired ratio of styrene to ethylbenzene. The output of this controller is fed simultaneously through the feed forward input of three summing amplifiers 74, 74 and 74" via line 73 whose output is finally transmitted to the temperature controller set points via line 75, 75 and 75 The output of the benzene memory amplifier 35 and toluene memory amplifier 36 is transmitted via lines 39 and 40 to a summing amplifier 46. The signal of summing amplifier 46 represents the sum of benzene and toluene and its signal is transmitted via line 41 to a divider 47. The output of the styrene memory amplifier 37 is transmitted via line 42 to the divider 47 and the output of the divider which represents the ratio of benzene plus toluene to styrene (B T)/S is transmitted via line 79 to an optimizer 80. The output in line 79 represents the performance signal of the reactor 51. The optimizer by introducing small perturbations into the control process via the temperature controllers 64, 64' and 64" notes the effct on the performance index B T)/S and determines an output signal necessary for each reaction zone to approach an optimum performance index (in this case a minimum). The output signals from the optimizer are transmitted via line 81, 87 and 88 to the summing amplifiers 74, 74 and 74". The signals from the summing amplifiers correspond to the set points of the temperature controllers 64, 64 and 64" and thus regulate the steam input and consequently the heat input into each catalytically active zones A, B, and C. Thus, the proportional controller 71 adjusts the set point of the temperature controllers 64 in response to a desired conversion level determined by the ratio of styrene to ethylbenzene in the conduit 53 and the optimizer80 adjusts each set point of the temperature controller 64, 64 and 64" by minimizing the ratio of the undesirable products of benzene to toluene to styrene in the product effluent.

As was the case in the embodiment of FIG. 1 of the drawing the small perturbations made by the optimizer for making a decision as to each reaction zone are preferably made out of sequence with each other. By mak ing the perturbations the optimizer can differentiate which perturbations in which reaction zone cause the performance index to change and thus make its decision as to each reaction zone. The signals from the proportional controller are the second component of the set points and of course correspond to a value which maintains the ratio of styrene to ethylbenzene within or about a desired range; e .g., 60 percent. Preferably, any changes made by the proportional controller are made out of sequence with any changes made by the optimizer so causes of any changes in the ratio (B T)/S are recognizable.

Referring now to FIG. 4 of the drawing there is shown a simplified schematic flow diagram for a typical catalytic reforming unit which utilizes the inventive control system. A low octane number feedstock comprising naphtha or gasoline boiling range hydrocarbon constituents, having an end boiling point of about 350 F enters the reforming process via line 100. A recycleinto a reactor preheater 104 which may be any type of heat exchanger employing any type of heating mediums such as steam, hot oil, hot vapor, flue gas, etc. Normally however, in order to achieve the high temperature required, preheater. 104 will be a direct fired furnace as illustrated. The reaction mixture of the hydrocarbon and hydrogen is heated within a coil 107 of preheater 104. The heated reaction mixture leaves preheater 104 via line 102, typically at a temperature of from about 900 to l,00O F depending upon the composition of hydrocarbon feedstock. The hot mixture charge stock. The reactor effluent passes via line 150 to a reheater 154 which may be similar to preheater 104. The effluent is heated within a coil 157. The reheated mixture leaves reheater 154 via line 152 typically at a temperature of from about 900 to l,000 F.

The hot mixture passes into a second reactor zone comprised of a reactor vessel 151 at a pressure of about 300 psig having suitable catalyst therein whereby such mixture undergoes a further conversion to lower boiling hydrocarbon constituents having a higher octane number. The reactor mixture leaves reaction zone 15] via line 103 at a somewhat lower temperature and passes into a heat exchanger wherein the mixture is cooled and normally liquid constituents are condensed. The condensed and cooled mixture leaves the heat exchanger 135 at a temperature of about 60 to 120 F, and passes into a separator 136 via line 137. Separator 136 will be at a pressure which is substantially the same pressure as the reaction zone, but it will be at a slightly lower level due to pressure drop through the reactors catalyst beds, line 150, heater 154, line 152, line 103, heat exchanger 135, and line 137. Thus, whereas the reactor 101 will typically be at an inlet pressure of about 300 psig, separator 136 will typically be at a pressure of about 250 psig or lower. The condensed and cooled effluent entering separator 136 via line 137 is separated therein into a vapor phase and a liquid phase. The vapor phase is withdrawn via line 99 for recycle to the reaction zones. Compressor means not shown, sends the hydrogen-rich vapor phase via line 99 into line 100 for mixture with the charge stock, as was previously set forth hereinabove. The catalytic reforming reaction not only upgrades the hydrocarbon constituents to higher octane number components, but it also produces hydrogen as a byproduct of the process. Consequently, a net hydrogen-rich gas is withdrawn via line 140 by conventional pressure control means, not shown, as a net gas product which is typically sent to further processing units for consumption elsewhere in the refinery. i V

.The liquid phase containing dissolved gaseous components is withdrawn from separator 136 via line 141 and is passed through a control valve 142 usually into a fractionation zone (not shown). The liquid phase withdraw rate typically is adjusted via a liquid level controller (not shown) which may be operated by a level sensing means in the separator. The level control ler would adjust valve 142 by transmitting a pneumatic, electrical, or hydraulic output signal.

Heat input to reaction zones is provided by introducing a fuel via lines 106 and 156 into burner 105 in the preheater 104 and burner of reheater 154 respectively. The fuel, which may be a liquid or gas, is burned within the combustion chambers and the hot combustion gases pass through the furnace and out of the stack. As the fuel is burned and the combustion gas passes through the furnace, it imparts the necessary heat input into the reaction mixture contained within the coils 107 and 157 by means of radiation and convection.

The heat input into the reaction mixture is controlled and adjusted by varying the flow of fuel to the burners 105 and 155. This control flow of fuel is achieved by means of a flow control loop similar to that shown in FIG. 1 of the drawing. The flow control loop of each reaction zone comprises control valves 108 and 108' and flow sensing means 109 and 109' which for illustrative purposes are shown as orifices. Flow signal lines 1 10 and 1 10' transmit the flow signals from the orifices 109 and 109 to flow controllers 112 and 112". Flow controllers 112 and 112' then transmit output signals to respective control valves 108 and 108' via lines 1 13 and 113'. The set point of flow controllers 112 and 112 are automatically adjustable.

Temperature controllers 114 and 114, also with an automatically adjustable or regulatable set points, sense the reactor inlet temperature as detected by thermocouples or other sensing means 115 and 115' located in the inlet lines 102 and 152 or other suitable inlet portions of the reaction zones. The resulting temperature output signals are transmitted from temperature controllers 114 and 114' to fluid controllers 112 and 112 via lines 117 and 117 60 adjust or reset the set points of each flow controller.

An octane monitor 118 which may be the type described in US. Pat. No. 3,463,613 issued Aug. 26, 1969 to ER. Fenske and J.l-l. McLoughlin is installed in line 143 connected with the liquid discharge of separator 136. It is connected through a suitable sampling line 119 to provide a continuous sample of the liquid phase of the reactor effluent. The sample is withdrawn and passed into the octane analyzer or monitor without intervening depressurization. Preferably, the octane monitor utilized a stabilized cool flame generator with a servo-positioned flame front. in a preferred embodiment, the flow of the oxidizer (air) and (fuel) effluent liquid phase sample are fixed, as is the induction zone temperature. Combustion pressure is the parameter which is varied in a manner to immobilize the stabilized cool flame front. Upon a change in sample octane number, the change in pressure required to immobilize the flame front within the octane monitor provides a direct indication of the change of octane number in the sample delivered to the combustion chamber of the octane monitor. Typical operating conditions for the octane monitor are:

Air flow Fuel flow Induction zone temperature Combustion pressure Octane range (max) The sample may be drawn off at a rate of about 100 cc per minute from a point upstream of the control valve 142 and returning it downstream from the control valve 142 the sample itself being drawn off from an intermediate portion of the sample loop and injected at a controlled rate by a metering pump to the combustion tube of the octane monitor.

The octane monitor output signal is transmitted via line 120 to a recorder controller 121. Upon a decrease in the measured octane number of the liquid phase sample, the octane monitor will call for an increase in the reaction zone temperature in order to dehydrogenate a greater proportion of the naphthenes in the charge stock, to produce a greater amount of high octane aromatic hydrocarbon in the effluent. Thus, the recordercontroller 121 will call for an increase in the flow of fuel which is done indirectly through summing amplifiers 124 and 124'. in other words, the output of the recorder controller 121 is connected via line 131 to summing amplifiers 124 and 124' and via lines 125 and 125' to the set point of the temperature controllers 114 and 114'. Summing amplifiers 124 and 124 combine the signal from the recorder controller 121 and the signals from an optimizer 130. Thus, considering only recorder controller 121, upon a decrease in the measured octane number of the liquid phase sample, the octane monitor will call for an increase in the reaction zone temperatures in both reaction zones in order to dehydrogenate a greater proportion of the naphthenes in the charge stock, to produce a greater amount of high octane aromatic hydrocarbons in the efiluent. Temperature controllers 114 and 114 then will call for an in crease in the flow of fuel to the heaters 104 and 154 in order to increase the heat input into the reactants in coils 107 and 157 and thereby increase the temperature of the reaction mixture entering the reaction zones.

If the octane number of the effluent sample is higher than the required specification, the octane monitor will call for a decrease in the reaction zone temperature and the overall corrective action will be the reverse of that previously described. The octane number of the liquid phase of the reactor effluent is continuously monitored and the reaction zone is controlled under conversion conditions sufficient to provide a substantially constant octane number on the liquid phase of the efiluent at a constant predetermined level.

Although maintaining the octane level of the liquid effluent is accomplished with the octance monitor and recorder controller 121, we have found that this control is not in itself adequate. In other words, maintaining the specification octane number may decrease the yield to such an extent that all savings in the utility costs will be cancelled. Thus, the present invention as another factor to adjust the set points of the temperature controllers and that being the signals derived from optimizer 130. Optimizer may be of the type previously described which introduces perturbations into the input of each reaction zone and notes the effect on the'perforrnance index it scans. In this particular embodiment, the performance index the optimizer scans is determined by the liquid yield. Accordingly there is provided a flow sensing means 143 in line 141 downstream of the separator 136, which for illustrative purposes is shown as an orifice. A flow signal line 144 transmits the flow signal from the orifice 143 to memory amplifier 145. Memory amplifier 145 transmits the peak rate of flow to the optimizer 130 via transmitting line 146 although an average or filtered ratio may be used. The optimizer in turn transmits output signals via lines 147 and 197 to summing amplifiers 124 and 124' respectively. Summing amplifiers 124 and 124 add the signals from line 147 and Y197 to the signal from line 131 and transmit these output signals via lines 125 and 125' to corresponding temperature controllers to ad just the set points thereof. Thus, considering only the optimizer portion of the control system, it is seen that the optimizer will sense a signal indicating the liquid yield quantity of flow. It will introduce small perturbations into each reaction zone via its output to the temperature controllers 114 and 114 which will vary the heat input into each reaction zone. The optimizer'will note whether the liquid yield will increase or decrease and subsequently transmit the individual output signals necessary to increase the liquid yield. It does not matter whether or not there actually exists a maximum condition of yield or at what point the maximum if any does exist. The optimizer merely transmits signals that will increase the yield. But, it will not increase the yield to the exclusive detriment of the octane value since the octane is being continually monitored and controlled by the recorder controller 121 preferably out of sequence with the optimizer.

The present invention should not be considered directed to merely a system where the heat input is controlled in order to control the severity of reaction but may be directed on the other hand, to systems where one of the components of the feed is the variable to control the severity of the reaction. Also, it is noted that the temperature controllers used only one sensing means to determine the severity of the reaction in all three embodiments It is also contemplated to use a temperature controller whose set point is determined by aAT across the reaction zone.

The method of operation of the inventive control system is readily apparent to those skilled in the art from the foregoing discussion relative to the drawing. In addition, the advantages of the present invention are equally apparent.

The primary advantage is that the present invention maintains a particular range of operation, e.g. percent conversion, octane level, and yet optimizes a related but not necessarily dependent performance index by regulating the severity of connecting reaction zones. Of

course it is to be considered to be within the scope of this present invention to provide the necessary relays, gates, timers, etc. to in turn compensate for lag times inherent in large reactor systems. In addition, it is not absolutely necessary that the signals from the optimizers and from the range of operation controllers be. added simultaneously as was set out previously. In other words, the range of operation controller may be set to update the temperature controller set point periodically, for example, every minutes, and the signal from the optimizer may be used to update the tempera ture controller set point every 60 minutes. Of course other time periods may be considered to be in the scope of this invention.

In the foregoing disclosure the use and application of the improved control system has been disclosed with reference to catalytic reforming and styrene production systems. Those skilled in the art realize, however, that the inventive control system is not so limited. The

inventive control system which has been disclosed.

herein may be utilized in any reaction process such as thermocracking, catalytic cracking, thermo hydrocracking, catalytic hydrocracking, isomerization, alkylation, polymerization, and the like.

Those skilled in the art realize that many conversions and processes employ plural reactor vessels with a preheater at each individual reaction vessel. Thus, it is within the scope of the present invention to apply an embodiment of the inventive control system to more than two or three of preheater-reactor combinations. For example, a catalytic reforming unit typically employs three or more reactor vessels and corresponding preheaters for three reactor catalytic reforming zones. The method of adapting the present invention to provide other multiple application of the inventive control system, would be readily apparent to those skilled in the art utilizing the teachings which have been presented hereinabove. I

Additionally, while the inventive control system has been disclosed with reference to the control of conversion or reaction severity or rate of reaction by the adjustment and control of heat input, e.g. (I) steam, (2) heaters, those skilled in the art realize that the inventive control system may be utilized to control severity or rate of reaction by the adjustment of any other operating variable. For example, in fluid catalytic cracking the inventive control system may be utilized to control the rate of catalyst circulation. In l-IF alkylation the inventive control system may adjust reaction severity by adjustments to the rate of circulation of isobutane reac- 5 tant. In polymerization over solid phosphoric acid catalyst, the inventive control system may adjust reaction severity by adjusting the rate of flow of olefin reactant to the reaction zone. In each instance, the adjustments to the conversion or reaction severity made by the inventive control system, will result in the production of the ultimate product within the specification, range of operation, and with the performance index optimizer therein.

The components of the control system shown in the drawings are well known to those skilled in the art. The various transmitting lines, transmitters, dividers, summing amplifiers, optimizers, sensing devices, etc. are available commercially from any number of reputable instrument manufacturers.

I claim as my invention:

1. In combination with at least two serially connected reaction zones having inlet means for introducing an inlet reactant stream thereto and outlet means for dis- 25 charging the resultant effluent therefrom, a control system which maintains a desired range of operation and optimizes the performance thereof comprising:

a. regulating means connected to each reaction zone for regulating the severity of reaction therein;

b. a control means connected to each regulating means for controlling the regulation thereof, each control means including a regulatable set point;

c. analyzing means communicating with the effluent of the downstream reaction zone for producing a signal responsive to the character of said effluent;

d. performance indicating means connected to said analyzing means for determining a performance index output signal;

e. optimizer means connected to the performance indicating means for optimizing the performance of said reaction zones, said optimizer means including means for determining a first output signal for each said control means and including computer means for analyzing the performance index output signal of said performance indicating means to determine said first output signal necessary for each reaction zone to approach an optimum performance of said reaction zones;

f. controller means connected to said analyzing means for determining a second output signal corresponding to the desired conversion level of said reaction zones; and,

g. summing means connected to said optimizer means, to said controller means, and to said control means for summing each first output signal and the second output signal to thereby generate signals representing each aforesaid regulatable set point. '2. The control system of claim 1 further characterized in that said performance index output signal is comprised of afunction of:

1. theundersirable products in said effluent with respect to 2. the desirable products in said effluent. 3. The control system of claim 1 further characterized in that said regulating means includes means to regulate the heat input to said reaction zones.

4. The control system of claim 1 further characterized in that the conversion level of said reaction zones is determined by a function of:

1. the desired products in said effluent with respect 2. the unreacted reactants remaining in said effluent.

5. The control system of claim 1 further characterized in that the conversion level of said reaction zones is determined by the octane rating of said effluent.

6. A method of controlling the operation of at least two serially connected reaction zones comprising the steps of:

a. regulating the reaction severity within each reaction zone;

b. controlling such regulation in response to a regulatable set point signal for each reaction zone;

0. analyzing the effluent of the downstream reaction zone to produce a signal responsive to the character of said effluent;

d. determining a performance index output signal from the signal derived from step (c);

e. optimizing the performance of said reaction zones by analyzing the output signal derived from step (d) and determining a first output signal necessary to approach an optimum performance of said reaction zones;

f. determining a second output signal corresponding to a desired conversion level of said reaction zones; and,

g. summing each of the first output signals with the second output signal to thereby generate each aforesaid regulatable set point signal.

7. The method of claim 6 wherein the performance index output signal is comprised of a function of:

l. the undesirable products in said effluent with respect to 2. the desirable products in said effluent.

8. The method of claim 6 wherein the second output signal of step (1) is derived from the conversion level determined by a function of:

1. the desired products in said effluent with respect 2. the unreacted reactants remaining in said effluent.

9. The method of claim 6 wherein the second output signal of step (f) is derived from the conversion level determined by the octane rating of said effluent.

10. The method of claim 6 wherein said reaction severity is regulated by regulating the heat input to each reaction zone.

11. In the process of dehydrogenating ethylbenzene wherein ethylbenzene admixed with steam is passed through at least two catalytic reaction zones and a total effluent including the desirable product styrene, the less desirable products of benzene and toluene, and unreacted ethylbenzene is discharged of benzene therefrom, a method of controlling such process whichcomprises the steps of:

a. regulating the reaction severity within each catalytic reaction zone;

b. controlling such regulation in response to a regulatable set point signal for each reaction zone;

c. analyzing the effluent of the downstream reaction zone to produce signals responsive to:

1. the quantity of benzene in said effluent;

2. the quantity of toluene in said effluent;

3. the quantity of styrene in said effluent;

4. the quantity of ethylbenzene in said effluent;

d. determining a performance index output signal from signals (1), (2), and (3) of step (c), the value of said performance index output signal being given by a function of:

1. the sum of the quantities of benzene and toluene .with respect to 2. the quantity of styrene in said effluent e. optimizing the performance of said reaction zones by anaylzing the performance index output signal of step (d) and determining a first output signal necessary for each reaction zone to approach an optimum performance of said reaction zones;

f. determining the total conversion level from signals (3) and (4) of step (c) the value of said total conversion level being given by a function of:

l. the quantity of styrene with respect to 2. the quantity of ethylbenzene in the effluent;

. determining a second output signal whose value is determined by the comparison of a desired total conversion level of said reaction zone to the actual total conversion level of each reaction zone determined in step (f);

h. summing each of the first output signals of step (e) with the second output signal of step (g) to thereby generate each aforesaid regulatable set point signal.

12. The process of claim 11 wherein step (a) includes regulating the input of superheated steam to said reaction zones.

13. In the process of reforming hydrocarbon charge stock, wherein the hydrocarbon charge stock is passed through at least two catalytic reaction zones and a total product effluent is discharged therefrom, a method of controlling such process which comprises the steps of:

a. regulatingthe severity of reaction within each catalytic reaction zone;

b. controlling such regulation in response to a regulatable set point signal for each reaction zone;

c. analyzing the effluent of the downstream reaction zone to produce signals responsive to:

1. the liquid yield in said product effluent; 2. the octane value of the liquid yield;

d. optimizing the performance of the reaction zones by analyzing signal (1) of step (c) and determining a first output signal necessary for each reaction zone to approach an optimum performance of said reaction zones;

e. determining a second output signal whose value is determined by the comparison of the desired octane value of the liquid yield and the octane value determined in step (c); and

f. summing each of the first output signals of step (d) with the second output signal of step (b) to thereby generate each aforesaid regulatable set point signal.

14. The process according to claim 13 wherein the severity of reaction is regulated by regulating the heat input to said reaction zones. 

1. In combination with at least two serially connected reaction zones having inlet means for introducing an inlet reactant stream thereto and outlet means for discharging the resultant effluent therefrom, a control system which maintains a desired range of operation and optimizes the performance thereof comprising: a. regulating means connected to each reaction zone for regulating the severity of reaction therein; b. a control means connected to each regulating means for controlling the regulation thereof, each control means including a regulatable set point; c. analyzing means communicating with the effluent of the downstream reaction zone for producing a signal responsive to the character of said effluent; d. performance indicating means connected to said analyzing means for determining a performance index output signal; e. optimizer means connected to the performance indicating means for optimizing the performance of said reaction zones, said optimizer means including means for determining a first output signal for each said control means and including computer means for analyzing the performance index output signal of said performance indicating means to determine said first output signal necessary for each reaction zone to approach an optimum performance of said reaction zones; f. controller means connected to said analyzing means for determining a second output signal corresponding to the desired conversion level of said reaction zones; and, g. summing means connected to said optimizer means, to said controller means, and to said control means for summing each first output signal and the second output signal to thereby generate signals representing each aforesaid regulatable set point.
 2. the desirable products in said effluent.
 2. The control system of claim 1 further characterized in that said performance index output signal is comprised of a function of:
 2. the unreacted reactants remaining in said effluent.
 2. the octane value of the liquid yield; d. optimizing the performance of the reaction zones by analyzing signal (1) of step (c) and determining a first output signal necessary for each reaction zone to approach an optimum performance of said reaction zones; e. determining a second output signal whose value is determined by the comparison of the desired octane value of the liquid yield and the octane value determined in step (c); and f. summing each of the first output signals of step (d) with the second output signal of step (b) To thereby generate each aforesaid regulatable set point signal.
 2. the quantity of ethylbenzene in the effluent; g. determining a second output signal whose value is determined by the comparison of a desired total conversion level of said reaction zone to the actual total conversion level of each reaction zone determined in step (f); h. summing each of the first output signals of step (e) with the second output signal of step (g) to thereby generate each aforesaid regulatable set point signal.
 2. the quantity of styrene in said effluent e. optimizing the performance of said reaction zones by anaylzing the performance index output signal of step (d) and determining a first output signal necessary for each reaction zone to approach an optimum performance of said reaction zones; f. determining the total conversion level from signals (3) and (4) of step (c) the value of said total conversion level being given by a function of:
 2. the quantity of toluene in said effluent;
 2. the unreacted reactants remaining in said effluent.
 2. the desirable prOducts in said effluent.
 3. the quantity of styrene in said effluent;
 3. The control system of claim 1 further characterized in that said regulating means includes means to regulate the heat input to said reaction zones.
 4. The control system of claim 1 further characterized in that the conversion level of said reaction zones is determined by a function of:
 4. the quantity of ethylbenzene in said effluent; d. determining a performance index output signal from signals (1), (2), and (3) of step (c), the value of said performance index output signal being given by a function of:
 5. The control system of claim 1 further characterized in that the conversion level of said reaction zones is determined by the octane rating of said effluent.
 6. A method of controlling the operation of at least two serially connected reaction zones comprising the steps of: a. regulating the reaction severity within each reaction zone; b. controlling such regulation in response to a regulatable set point signal for each reaction zone; c. analyzing the effluent of the downstream reaction zone to produce a signal responsive to the character of said effluent; d. determining a performance index output signal from the signal derived from step (c); e. optimizing the performance of said reaction zones by analyzing the output signal derived from step (d) and determining a first output signal necessary to approach an optimum performance of said reaction zones; f. determining a second output signal corresponding to a desired conversion level of said reaction zones; and, g. summing each of the first output signals with the second output signal to thereby generate each aforesaid regulatable set point signal.
 7. The method of claim 6 wherein the performance index output signal is comprised of a function of:
 8. The method of claim 6 wherein the second output signal of step (f) is derived from the conversion level determined by a function of:
 9. The method of claim 6 wherein the second output signal of step (f) is derived from the conversion level determined by the octane rating of said effluent.
 10. The method of claim 6 wherein said reaction severity is regulated by regulating the heat input to each reaction zone.
 11. In the process of dehydrogenating ethylbenzene wherein ethylbenzene admixed with steam is passed through at least two catalytic reaction zones and a total effluent including the desirable product styrene, the less desirable products of benzene and toluene, and unreacted ethylbenzene is discharged of benzene therefrom, a method of controlling such process which comprises the steps of: a. regulating the reaction severity within each catalytic reaction zone; b. controlling such regulation in response to a regulatable set point signal for each reaction zone; c. analyzing the effluent of the downstream reaction zone to produce signals responsive to:
 12. The process of claim 11 wherein step (a) includes regulating the input of superheated steam to said reaction zones.
 13. In the process of reforming hydrocarbon charge stock, wherein the hydrocarbon charge stock is passed through at least two catalytic reaction zones and a total product effluent is discharged therefrom, a method of controlling such process which comprises the steps of: a. regulating the severity of reaction within each catalytic reaction zone; b. controlling such regulation in response to a regulatable set point signal for each reaction zone; c. analyzing the effluent of the downstream reaction zone to produce signals responsive to:
 14. The process according to claim 13 wherein the severity of reaction is regulated by regulating the heat input to said reaction zones. 